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|Title:||The Gaia-ESO Survey: New constraints on the Galactic disc velocity dispersion and its chemical dependencies||Authors:||Guiglion, G.
de Laverny, P.
Wyse, R. F. G.
RANDICH, Maria Sofia
Koposov, S. E.
Costado, M. T.
SACCO, GIUSEPPE GERMANO
Worley, C. C.
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||583||First Page:||A91||Abstract:||Context. Understanding the history and the evolution of the Milky Way is one of the main goals of modern astrophysics. In particular, the formation of the Galactic disc is a key problem of Galactic archaeology. <BR /> Aims: We study the velocity dispersion behaviour of Galactic disc stars as a function of the [Mg/Fe] ratio, which for small metallicity bins can be used as a proxy of relative age. This key relation is essential to constrain the formation mechanisms of the disc stellar populations as well as the cooling and settling processes. <BR /> Methods: We used the recommended parameters and chemical abundances of 7800 FGK Milky Way field stars from the second internal data release of the Gaia-ESO spectroscopic Survey. These stars were observed with the GIRAFFE spectrograph (HR10 and HR21 setups), and cover a large spatial volume in the intervals 6 <R< 10 kpc and | Z | < 2 kpc. Based on a chemical criterion, we separated the thin- from the thick-disc sequence in the [Mg/Fe] vs. [Fe/H] plane. <BR /> Results: From analysing the Galactocentric velocity of the stars for the thin disc, we find a weak positive correlation between V<SUB>φ</SUB> and [Fe/H] that is due to a slowly rotating [Fe/H]-poor tail. For the thick disc stars, a strong correlation with [Fe/H] and [Mg/Fe] is established. In addition, we have detected an inversion of the velocity dispersion trends with [Mg/Fe] for thick-disc stars with [Fe/H] < -0.10 dex and [Mg/Fe] > +0.20 dex for the radial component. First, the velocity dispersion increases with [Mg/Fe] at all [Fe/H] ratios for the thin-disc stars, and then it decreases for the thick-disc population at the highest [Mg/Fe] abundances. Similar trends are observed for several bins of [Mg/Fe] within the errors for the azimuthal velocity dispersion, while a continuous increase with [Mg/Fe] is observed for the vertical velocity dispersion. The velocity dispersion decrease agrees with previous measurements of the RAVE survey, although it is observed here for a greater metallicity interval and a larger spatial volume. <BR /> Conclusions: Thanks to the Gaia-ESO Survey data, we confirm the existence of [Mg/Fe]-rich thick-disc stars with cool kinematics in the generally turbulent context of the primitive Galactic disc. This is discussed in the framework of the different disc formation and evolution scenarios. <P />Based on observations collected with the FLAMES spectrograph at the VLT/UT2 telescope (Paranal Observatory, ESO, Chile), for the Gaia-ESO Large Public Survey, programme 188.B-3002||Acknowledgments:||We are grateful to the referee for the constructive comments that have helped us to improve our paper. G. Guiglion and A. Recio-Blanco thank Paola di Matteo and Misha Haywood for their careful reading of the paper and constructive comments. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia -ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’ Istruzione, dell’ Università’ e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012”. The results presented here benefit from discussions held during the Gaia -ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. A. Recio-Blanco, P. de Laverny and V. Hill acknowledge the “Programme National de Cosmologie et Galaxies” (PNCG) of CNRS/INSU, France, for financial support.||URI:||http://hdl.handle.net/20.500.12386/23102||URL:||https://www.aanda.org/articles/aa/abs/2015/11/aa25883-15/aa25883-15.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201525883||Bibcode ADS:||2015A&A...583A..91G||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Oct 28, 2020
checked on Oct 28, 2020
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